Some types of vehicles installed with an engine stop-and-start system, such as an idle reduction control system, have been recently developed for reduction in fuel cost, in exhaust emission, and the like. Such engine stop-and-start systems are designed to, in response to a driver's engine stop operation, shut off fuel supplied to an internal combustion engine of a vehicle so as to automatically stop it. After the stop of the internal combustion engine, these engine stop-and-start systems are designed to cause, in response to a driver's Operation to restart the vehicle, a starter to crank the internal combustion engine, thus restarting the internal combustion engine.
In normal starters, a pinion is shifted by an actuator toward a ring gear coupled to a crankshaft of an internal combustion engine to be engaged with the ring gear. While being meshed with the ring gear, the pinion is rotatably driven by a motor so that the crankshaft is rotated. This, cranks the internal combustion engine.
In conventional normal starters, when an internal combustion engine is restarted, the actuator and motor are designed to be simultaneously driven to carry out the engaging process of the pinion with the ring gear. The structure may produce, when the pinion is shifted to be engaged with the ring gear, loud noise due to the strike and/or the friction therebetween. This may be irritating and unpleasant for the occupant(s), and/or may delay a time required to restart the internal combustion engine by a time required for the pinion to be engaged with the ring gear. The latter problem may cause the occupant(s) to feel acceleration at the engine restart insufficient.
In order to address these problems, U.S. Pat. No. 7,275,509 corresponding to Germany Patent Application Publication No. DE 10 2005 049 092 and to Japanese Patent Application Publication No. 2007-107527 discloses a system for a starter of an internal combustion engine.
The disclosed system, referred to as “first system”, is designed such that the motor and actuator of a starter are separately drivable. During the internal combustion engine being automatically run down, in other words, during the crankshaft (engine) coasting (being rotated without the aid of the internal combustion engine), when the rotational speed of the internal combustion engine drops into a very low-speed range of 300 RPM or less, more specifically, 50 to 100 RPM, the first system drives the actuator to thereby shift the pinion to be meshed with the ring gear.
The first system is also designed to address the following problem. Specifically, immediately before the stop of the forward rotation of the internal combustion engine, because the piston of the engine does not pass the top dead center of a cylinder, the engine is reversely rotated. During the reverse rotation of the engine, when the pinion is shifted to be engaged with the ring gear, the engagement may produce loud noise due to the impact and/or the friction therebetween. This may be irritating and unpleasant for the occupant(s).
In order to solve the problem, the first system is equipped with a first sensor and a second sensor each designed as a normal magnetic-pickup type crankshaft sensor.
Each of the first and second sensors includes a reluctor disk coupled to the internal combustion engine. The reluctor disk includes an alternating arrangement of teeth and tooth spaces. Each of the first and second sensors is designed to pick up a change in a previously formed magnetic field according to the rotation of the teeth of the reluctor disk (crankshaft) to thereby generate a pulse signal; this pulse signal consists of a train of pulses (each pulse is a transition of a base signal level to a preset signal level). Each of the pulses is detected by each of the first and second sensors when one tooth of the rotating reluctor disk passes in front of a corresponding one of the first and second sensors.
The first system receives the pulse signal generated by each of the first and second sensors, and grasps the rotational speed of the internal combustion engine based on intervals between the pulses of the pulse signal generated by at least one of the first and second sensors.
The rotational direction of the crankshaft is ascertained by utilizing: one of a rising and falling edge of one pulse of the pulse signal of one of the first and second sensors; and a signal level (the base signal level or preset signal level) of the electrical signal of the other of the first and second sensors.
The first system drives the actuator to shift the pinion to be engaged with the ring gear when: the rotational speed of the internal combustion engine drops into the very low-speed range; and the rotational direction of the crankshaft corresponds to the forward rotational direction.
Additionally, US Patent Application Publication No. 2008/0127927 corresponding to WO Publication No. 2006/018350 and to Published Japanese translation No. 2008-510099 of the WO Publication No. 2006/018350 discloses a device for starting an internal combustion engine.
The disclosed device is provided with an ECU for controlling the actuator and motor of a starter, and a current adjuster for adjusting the level of a current to be supplied to the actuator.
The disclosed device uses a normal magnetic-pickup type crankshaft sensor set forth above so that the ECU receives the pulse signal generated by the crankshaft sensor, and detects the rotational speed of the internal combustion engine based on intervals between the pulses of the pulse signal generated by the crankshaft sensor.
During the internal combustion engine being automatically run down, when the rotational speed of the internal combustion engine drops to be lower than a preset threshold, the ECU controls the current adjuster to activate the actuator by an adjusted low current to shift the pinion to be engaged with the ring gear. Thereafter, after the rotation of the crankshaft has been completely stopped, the ECU activates the motor to rotate the pinion, thus cranking the internal combustion engine.
Furthermore, Japanese Patent Application Publication No. H11-030139 discloses an engine stop and start system.
The disclosed system, referred to as “second system”, is equipped with such a normal magnetic-pickup type crankshaft sensor for measuring the rotation of the crankshaft of an internal combustion engine. The second system is designed to, when the crankshaft sensor measures that the rotation of the crankshaft of the internal combustion engine is completely stopped, activate the actuator of a starter by a low voltage to shift the pinion to be engaged with the ring gear.